A great quantity of integrated circuits are currently being used in electronic apparatuses. Many of the integrated circuits used in electronic apparatuses are Application-Specific Integrated Circuits (ASIC), and are dedicated circuits designed for specific electronic apparatuses. Among these application-specific integrated circuits, the arrangement of cells (logic circuits such as AND circuits and OR circuits) and connections between cells are carried out in the process of fabricating the integrated circuits and the circuit configuration therefore cannot be altered after fabrication.
In recent years, competition in the development of electronic apparatuses has become fierce, and further, progress is being made in the miniaturization of electronic apparatuses. Under these circumstances, attention has focused on programmable logic in which the circuit configuration can be altered by electronic signals even after fabrication to allow many functions to be offered by means of a single chip. Programmable logic is of a configuration in which a plurality of logic cells are connected together by way of a switching elements. Logic cells are logic circuits that serve as the units by which programmable logic is assembled. Representative examples of programmable logic include FPGA (Field-Programmable Gate Arrays) and DRP (Dynamically Reconfigurable Processors).
Although programmable logic has been attracting attention, the incorporation of programmable logic in electronic apparatuses is still limited. There are several reasons for this limitation. First, in programmable logic to date, the switching elements that provide mutual connections between logic cells are large and have high ON resistance. In response to this problem, programmable logic to date has been of configurations that employ few logic cells having a large number of transistors and that minimize these switching elements, which are large and have high ON resistance. These constraints limit the degree of freedom of the combination of logic cells and limit the functions of the programmable logic that can be offered. In other words, the large size and high ON resistance of switching elements have limited the functions of the programmable logic and have limited the range of application of incorporation of programmable logic in electronic apparatuses.
Diversifying the functions of programmable logic and promoting the incorporation of programmable logic in electronic apparatuses calls for both reducing the size of the switching elements that interconnect logic cells and reducing the ON resistance of these elements. As a device that can meet these conditions, a switching element (hereinbelow referred to as a “metal atom-mobile switching element”) that uses metal ion movement in an ion conductor (a material in which ions can move freely) and an electrochemical reaction is proposed in JP-A-2002-536840. A metal atom-mobile switching element is known to be smaller and have lower ON resistance than semiconductor switching elements (such as MOSFETs) that have until now been widely used in programmable logic.
FIG. 1 is a schematic view for explaining a metal atom-mobile switching element of the related art. The metal atom-mobile switching element shown in FIG. 1 is a metal atom-mobile switching element made up from an ion conduction layer composed of an ion conductor (Cu2S), a first electrode (Ti) that contacts the ion conduction layer, and a second electrode composed of metal (Cu) that contacts the ion conduction layer and that serves as a supply source of metal ions (Cu+). The materials that make up each part are offered as examples.
When negative voltage is applied to first electrode (Ti) with second electrode (Cu) as a basis of the voltage, metal ions (Cu+) ion conduction layer in the vicinity of the contact surface with the first electrode (Ti) are reduced and metal (Cu) precipitates at the surface ion conduction layer that contacts the first electrode (Ti). In response to the precipitation of metal (Cu), the metal (Cu) of the second electrode oxidizes, dissolves in the ion conduction layer in the form of metal ions (Cu+), and maintains the balance of negative and positive ions within the ion conduction layer. The precipitated metal (Cu) grows in the direction of the second electrode (Cu) within the ion conduction layer. When the precipitated metal (Cu) contacts the second electrode (Cu), the switching element achieves the conductive (ON) state (refer to the left side of FIG. 1).
On the other hand, the application of a positive voltage to the first electrode (Ti) with the second electrode (Cu) as a basis of the voltage, produces the absolute opposite electrochemical reaction. As a result, metal (Cu) that extends from the first electrode (Ti) to the second electrode (Cu) is cut, and the switching element enters the nonconductive (OFF) state (see the right side of FIG. 1).
As described in the foregoing explanation, the metal atoms that make up the second electrode move between the first electrode and the second electrode in the form of a precipitate due to an electrochemical reaction, and in the conductive (ON) state form a metal interconnect that electrically connects the first electrode and the second electrode.